Electrode spacer



Feb. 9, 1943. c. P. VOGEL 2,310,662

ELECTRODE sPAcEE Filed Feb. 5, 1942 INVENTOR Char/e5 Vogel.

ATTUENEY Patented Feb. 9, 1943 ELECTRODE SPACER Charles P. Vogel, Millburn, N. J., assignor to Radio Corporation of America, a. corporation of Delaware Application February 5, 1942, Serial No. 429,593

Claims. (01. 250-275) My invention relates to electron discharge devices, particularly to means for accurately pacing the electrodes in such devices.

The usual electrode assembly of an electron tube comprises an assembly of cathode, grid and anode electrodes, supported at their ends in insulated spacers. Because of bowing and lateral or sideway movement of the electrodes caused by heat expansion, mechanical vibration and manufacturing tolerances, there exists a minimum practical spacing between electrodes when the electrodes are made to such dimensions as are required to obtain desirable electrical characteristics. It is difiicult in conventional structures of moderate size requiring close spacing between electrodes to make the electrodes individually structurally rigid and also retain the desired electrical characteristics. For example, in tubes designed to deliver 20 to 100 watts radio frequency output power with plate voltages as low as 500 volts it becomes desirable to space the control grid as close to the emitting surface as mechanical consideration will permit. However, the minimum practical spacing between grid and cathode. in tubes of this size, using conventional methods of support, is .025" where filamentary cathodes are used and .015" where indirectly heated cathode sleeves are used. The .025 spacing requires that electrodes with large areas be used to obtain the required power. Smaller spacings would permit reductions in the size of electrode areas.

An object of my invention is an electrode assembly that has closely but permanently and positively spaced electrodes, and that is easy to assembly in manufacture.

The characteristic features of my invention are defined in the appended claims and one embodiment thereof is described in the following specification and shown in the accompanying drawing in which Figure 1 shows partly in section an lectrode assembly constructed according to my invention with an indirectly heated cathode sleeve, Figure 2 is a cross sectional view of the assembly along the lines 22 of Figure 1, Figur 3 is a detailed perspective view of the electrodes assembled according to my invention, and Figures 4 and 5 show, respectively, the side and end views of an electrode assembly with a filamentary cathode embodying my invention.

The electrode assembly of Figure 1 comprises cathode I, concentric with a conventional control grid helix 2, wound on side rods 3, and the tubular anode 4, the electrodes each being supported, preferably, at both ends in end spacers 5. When the anode is relatively heavy as when made of graphite, it may be supported on a collar strapped to the stem of the envelope. The cath-v ode l, illustrated in Figure 1, is of the indirectly heated type comprising a sleeve exteriorly coated with an electron emissive material. Alternatively, the cathode may be of the common directly heated filamentary type as shown at la in Fig- Lu'es 4 and 5.

The characteristic feature of this electrode assembly, according to my invention, is means to permanently and accurately space each grid wire from the surface of the cathode. My novel spacing means comprises a wire helix, supported on side rods 1 much in the manner of a conventional wire wound grid, and coated with a refractory insulating material, such as sprayed and fused alumina or magnesia ceramic. When the cathode is of the indirectly heated sleeve type, it is preferably flattened as shown so that the planes of flattened turns of the control grid and of the insulated helix may be placed close to and effective over a considerable portion of the cathode. When the cathode is filamentary, the legs of a V or an M-shaped ribbon are arranged in a single plane so that the grids may be placed in closely spaced relation with the filament. The side rods 1 of the insulated helix are preferably quite small and the turns are formed so as to lie lightly against the surface of the cathode sleeve or against the edge of the filament ribbon. The grid turns likewise are flattened and formed to lie with a slight pressure against the insulated turns 6. The grid wires are disposed at an angle to the insulated turns so that the grid wires will not slip between the insulated turns and against the cathode. The grid wires, hence, are permanently spaced from the cathode surface a distance equal to the thickness of the insulated wire. The angle between wires may be obtained by winding one helix with a dilferent pitch than the other, by winding the helices with right hand and left hand turns, respectively, or by axially displacing the side rod or one of the helices. The angle between the wires and their pitch will of course determine the number of cross-over points or points of contact between wires.

The insulated helix 6 may be connected to a separate lead-in conduct-or or connected internally of the tube to the cathode. By applying the proper negative potential to the insulated helix, electron emission from the cathode to the control grid side rods may be prevented and the electrons may be biased into beams normal to the flattened surface of the cathode between the control grid wires.

In manufacture, the insulated helix 6 may first be telescoped over the cathode by pressing the side rods 7 together to spring the turns outwardly, care being taken to not distort the wires enough to crack the insulation. When the side rods 1 return to their normal position and are anchored at their ends in end spacers 5, the insulated turns lie lightly but firmly bear against the cathode. The side rods 3 of the control grid may be compressed in like manner and passed over the cathode and insulated helix assembly and mounted with the anode in the spacers 5.

My improved electrode assembly insures permanent close spacing between the electrodes and is easy to assemble in manufacture.

I claim:

1. An electron discharge device comprising an elongated cathode, a plurality of spaced parallel wires covered with an electrical insulating coating, the insulated wires being disposed across and in contact with the side of said cathode, a plurality of spaced parallel control grid wires in a plane parallel to the plane of the insulated wires, the grid wires being disposed at an angle to the insulated wires, the insulated and the rid wires being in contact at their cross-overpoints, and an anode outward from said control wires.

2. An electron discharge device comprising an elongated cathode, a helix supported on parallel rods telescoped over said cathode, the convolutions of said helix being covered with an inon rods telescoped over the first mentioned helix,

the convolutions of the control grid being disposed at an angle to the convolutions of the insulated helix, the wires of the two helices being in contact at their cross-over points and a tubular anode telescoped over said control grid.

3. An electron discharge device comprising an elongated cathode, an anode, a control grid consisting of a plurality of spaced parallel wires between the cathode and the anode, and a plurality of spaced insulated wires between the grid and the cathode, said insulated wires being angularly disposed with respect to the grid wires and in contact with the cathode and the grid wires.

4. An electron discharge device comprising a cathode with an extended electron emissive area, said area being substantially flat, a plurality of side-by-side control grid wires in a plane close to and parallel with the cathode area, and means for permanently and fixedly maintaining the spaced relation between said cathode and grid wires comprising a plurality of spaced insulated wires lying against said cathode and angularly disposed to said grid wires and in contact with the grid Wires at their cross-over points.

5. An electron discharge device comprising a filamentary cathode with a, plurality of electron emissive filaments arranged in one plane, a plurality of control grid wires arranged, in a plane closely spaced to and parallel with said one plane, and means for spacing said grid and filament comprising a plurality of insulating wires between the grid and cathode, and angularly crossing the filament and the grid wires.

CHARLES P. VOGEL. 

